This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2000-241285 filed on Aug. 9, 2000 and No. 2001-226613 filed on Jul. 26, 2001, the entire content of which is incorporated herein by reference.
The present invention generally relates to an unlock operation system. More particularly, the present invention pertains to an unlock operation system detecting an approach of a vehicle user to a vehicle door for unlocking the door when the user performs a door opening operation.
A known system disclosed in EP1006028 detects a condition that a person (i.e., a vehicle user; e.g., a driver) approaches or leaves a vehicle door and automatically locks or unlocks a lock mechanism provided in the vehicle door. The user carries a remote controller. A transmitting circuit, a receiving circuit, and a control portion are disposed in the vehicle. An antenna is disposed in a door handle of the vehicle door. The transmitting circuit transmits a request signal to the remote controller via the antenna. The transmitting circuit includes a resonant circuit. On the contrary, when the remote controller receives the request signal, the remote controller transmits a signal including an ID information to the receiving circuit of the vehicle. The ID information includes an intrinsic ID. The ID information including the intrinsic ID which is received at the receiving circuit and corresponding intrinsic ID memorized in the control portion in advance are compared in the control portion. By judging whether the intrinsic ID""s of the remote controller and the control portion match one another, the control portion locks or unlocks a door lock mechanism provided in the vehicle depending upon the user""s intention.
A Japanese Patent Laid-Open Publication No. H10-308149 discloses a system that includes a sensor in a door handle of a vehicle door for detecting the approach of a user. This sensor is resonated by a resonant circuit. When the user approaches the vehicle, a capacitance between the user and the vehicle door is changed. The user""s action for opening the vehicle door is detected by observing the change of the capacitance.
In order to improve the safety and convenience of the vehicle door lock device, it is preferable to combine the aforementioned two known systems. However, the resonant circuit included in the transmitting circuit and the resonant circuit for resonating a sensor electrode require respective oscillators. Using two oscillators increases the amount of electric current supplied through the oscillators and as is the case with the size of an overall circuit of the system.
In general, electric power is supplied from a battery to a movable body such as vehicle. It is required to detect the approach of the user even when an ignition switch is off such as when the vehicle is parked, in this automatic type of system. In order to use limited battery capacity effectively, it is desirable to restrain the electric power consumption of the system as much as possible.
It is an object of the present invention to provide an unlock operation system of a vehicle door having control means which can actuate a plurality of resonant circuits effectively.
In order to obtain the foregoing object, the unlock control system for a vehicle door lock mechanism comprises first resonant means resonating at a first value Q for transmitting a first signal to the outside of the vehicle; second resonant means for resonating at a second value Q which is greater than the first value Q, connected in series with the first resonant means and having a capacitance, a resonant condition being changed in accordance with a change of the capacitance; sole actuating means for actuating the first and the second resonant means; and control means for activating the first and the second resonant means alternatively and for unlocking the door lock mechanism in accordance with the change of the resonant condition of the second resonant means.
The effects of the present invention are as follows: Because the first resonant means and the second resonant means are connected in series, an impedance Zon of overall first and second resonant means can be expressed as Zon=j/xcfx89C1xc2x7(xcfx892C1L1xe2x88x921) when the switching means is ON; wherein C1 indicates a resonant capacitance of the first resonant means, L1 indicates a resonant inductance, and C2 indicates a resonant capacitance of the second resonant means. When the switching means is OFF, the impedance Zoff of the overall first and second resonant means can be expressed as Zoff=1/jxcfx89xc2x7(1/C1+1/C2)+jxcfx89xc2x7(L1+L2). By making the value Q (Q2) of the second resonant means far greater than the value Q (Q1) showing sharpness of resonance of the first resonant means (i.e., Q1 less than  less than Q2), the inductance L2 becomes far greater than inductance L1. Because the first and second resonant means share the single actuating means, the frequency thereof is constant, and accordingly the capacitance C1 becomes far greater than C2 (i.e., C1 greater than  greater than C2). When the switching means is OFF, the impedance Zoff of the overall resonant circuit can be approximated as Zoff=j/xcfx89C2xc2x7(xcfx892C2L2xe2x88x921). The impedance Zoff obtained by the above formula is presumed to be the same as a resonant circuit formed by C2L2 when the switching element is OFF. On the other hand, when the switching element is ON, the impedance Zon of the overall resonant circuit becomes Zon=j/xcfx89C1xc2x7(xcfx892C1L1xe2x88x921) to be a resonant circuit of C1L1. Accordingly, when the switching means is ON, only the impedance of the first resonant means exists and when the switching means is OFF, only the impedance of the second resonant means exists. That is, even when the first resonant means and the second resonant means are connected in series and actuated by the single actuating means, one of the impedance of the resonant means can be negligible and the other resonant means is not affected by the resonant condition of one of the resonant means.